Zapier integration - not all fields seem to be available

I'm building a Zapier integration which sends a GMail after form submission.

It works pretty well.

For some reason most but not all of the important fields in the knack table are available to be mapped to my GMail message.

Is there a trigger for Zapier to select certain fields from the knack table? It doesn't appear to be any particular sequence. I've got 8 out of the 9 desired fields available. Just wondering if there a way getting the ninth one. The table itself has about 40 fields.